Aldehyde, chrome and polyhydric alcohol tanned collagen articles and their production



Jan. 19, 1965 J. KURILLA CHROME AN ALDEHYDE D POLYHYDRIC ALCOHOL TANNECOLLAGEN ARTICLES AND THEIR PRODUCTION 2 Sheets-Sheefl Filed May 29,1963 INVENTOR. Aw/v Af/E/AAA KURILLA 9 POLYHYDRIC ALCOHOL TANNED 2Sheets-Sheet 2 Jan. 19, 1965 Filed May 29, 1963 INVENTOR. 7oA9v 17/244,:

1 g %//A/- ORNEYS United States Patent 3,l66,tl74 nnnnrnznn, orator r:AND eorrnrnnro Asco- HQL TANNED (IQLLAGEN ARTIQLEfi) AND The presentinvention relates to the treatment of protein material and the productso obtained with particular emphasis on the method of chemicallytreating substantially pure collagen filaments and strands for surgicaluses such as suturing and ligating.

This application is a continuation-in-part of application Serial No.85,362, filed January 27, 1961.

For the sake of clarity, the terms used herein are defined as follows:

The term tendon collagen fibril as used herein means a thread-likecollagen structure derived from beef tendon that is round in crosssection. These fibrils in the completely dehydrated state measure about500 to 2000 Angstroms in diameter.

The term swollen tendon collagen fibril as used herein means a collagenfibril derived from beef tendon that has been swollen in acid solution.The diameters of swollen collagen fibrils range from less than 5000Angstroms to about 90,000 Angstroms.

The term monofilarnent as used herein means a single thread of orientedcollagen fibrils as extruded through a single orifice in a spinnerette.

The term multifilament as used herein means a group of individualseparate filaments extruded through a spinnerette.

The term strand as used herein means a group of filaments that have beenunited to form a unitary structure.

The protein collagen has exceptional tensile strength and is essentiallynon-antigenic, which properties have resulted in the wide use ofsubstantially pure collagen strands in surgery. It is well known thatcollagen sutures which have been implanted in the human body are slowlyattacked by proteolytic enzymes with a resulting decrease in tensilestrength and ultimate absorption. It is also known that the rate ofabsorption can be controlled by treating the collagen strand withchemical reagents such as chromium salts. Thus, chromium treated sutureshave been prepared from sheep intestines which retain onehalf of theiroriginal tensile strength from 7 to 10 days after implantation.

A particular problem exists, however, in the case 0 extruded collagenstrands. lthas been noted that collagen strands obtained by extruding adispersion of'collagen fibrils into a coagulating bath are characterizedby a rapid in vivo digestion. Thus, a collagen suture prepared underconditions that involve swelling collagen fibrils in acid solution,extruding the swollen collagen fibrils to form a filament andsubsequently dehydrating the swollen collagen fibrils is more rapidlyattacked by proteolytic enzymes than sutures prepared from sheepintestines.

' It is an object of the present invention, therefore, to chemicallymodify collagen and thereby increase its resistance to enzymaticdegradation.

it is another object of the invention to provide 'a chemically treatedextruded colagen suture having a suitable wet tensile strength.

Still another object of the invention is to produce an extrudedchemically treated absorbable collagen suture that will retainsufficient tensile strength under the conditions of use to accomplishits purpose and be absorbed in the body after the wound has healed whenthe suture is no longer necessary. 7

The present invention provides a method of'chem-ically treating acontinuously extruded collagen strand to provide the desired strength,in vivo digestion time and uniformity of product. The process ischaracterized by treating a bonded collagen multifilament consecutivelywith at least two different solutions. The first solution is a solutionof a polyhydric phenol such as pyrogallol and/or an oxidized polyhydricphenol such as 1,4-naphthaquinone and the second solution is an acidsolution of a chromium salt and an aldehyde such as formaldehyde. Theuse of a third solution containing an alkaline solution of formaldehydeto treat the moving strand is optional.

The first solution of polyhydric phenol and/ or quinone, if used alone,provides a collagen strand which has inadequate initial wet strength andwhich has an excessively rapid rate of in vivo tensile strength loss.However, when this treatment is followed by the second solutioncontaining formaldehyde, the said rate is decreased. It is known thatformaldehyde alone will increase the intial wet strength of collagen,but if formaldehyde alone is used in the amount required for adequate invivo properties, the strand is embrittled and the knot strength islowered. By treating the strand consecutively with a polyhydric phenoland/or quinone solution and a formaldehyde solution, the rate of tensilestrength loss may be greatly improved without embrittling the strand.

The purpose of the chromium in the second bath is to increase the intialwet tensile strength of the final strand. Chromium alone has only aminor effect on the rate of tenshe strength loss of the collagen at theconcentration employed in the present invention.

a it will be understood by those skilled in the art that equivalentresults would be obtained if the order of the solutions were reversedand the collagen was first treated with a chromium formaldehyde solutionand then treated with the polyhydric phenol and/0r quinone solution.Also, the formaldehyde and chromium can be applied separately indifferent solutions. 7

The invention will appear more clearly from the following detaileddeseription when taken in connection with the accompanying drawings,which show by way of example, preferred embodiments of the inventiveidea. Referring now to the drawings,

FIGURE 1 illustrates a machine designed to continuously tan a bondedcollagen multifilament.

FIGURE 2 is a detailed perspective view of apart of the machineillustrated in FIGURE 1 showing the godet 21 which takes up the tapefrom the supply reel. This figure also shows the auxiliary roller 31which is associated with the godet 21. 7

FIGURE 3 is a perspective view of a false twister which is used to roundand shape the strand.

The starting material for the process of the present invention is abonded collagen multifilament which will be referred to hereafterascollagen tape. This material is ribbon-like in form and is made up offrom about 20 to about 500 individual collagen'multifilaments. Collagentape may be prepared by extruding a dispersion of substantially pureswollen tendon collagen fibrils through a multi-orifice spinnerette intoan alkaline acetone dehydrat ing bath. The multifilaments, as theyemerge from the spin bath, are very loosely united and are approximatelycircular in cross-section; however, the filaments are drawn from thespin bath by a rotating godet and the tension on the still Wet filamentsas they pass over the godet sur- I face bonds the individual filamentstogether to form a ribbon-like strand. When the bonded multifilament isdried, the ribbon-like shape is retained. it will be understood from theforegoing that the individual filaments are a bonded together bycohesive forces to form the collagen tape.

The mechanical handling of the collagen'tape as it passes through thedifferent tanning solutions and is dried and rounded to form a strand ofcircular cross-section is best illustrated by FIGURE 1. The machine tobe described has been designed for the continuous treatment of collagentape containing about 195 individual filaments and shaping the tannedmultifilament to form a rounded strand about 14.5 mils in diameter, butit will be understood that strands of smalleror larger diameter may beproduced by varying the number of individual filaments in the collagentape and such modifications are well within the scope of this invention.

It will be noted from FIGURE 1 that the collagen tape 11 is transferredfrom the supply reel 12 to the take-up spool 13 by the driven godets 21,22 and 23. The tape is stretched between godet21 and godet 22, and isstretched again between godets 22 and 23. Directly below each godet areauxiliary nylon rollers 31, 32 and 33. The rollers 31 and 32 aresurrounded by trays 14 and 15 which may be filled with liquids 41 and 42that are to be applied to the moving collagen strand. Other means oftreating the moving collagen strand with liquids are provided by thejets 20, 24 and 25.

The tubes'l, 17 and 18 are heated and function to dry and warm themoving strand. The desired circular crosssection of the final product cmbe accomplished by means of afalse twister 19 which operates to roundand dry the strand as it moves through the drying tubes.17 and 13.

The three godets 21, 22 and 23 may be made of nylon and each ispreferably 3 inches in circumference. All three godets are driven by aReeves variable speed gear reduction motor having an output speed rangeof 3.3 to 32.1 r.p.m. Directly below godet 21 is an auxiliary nylonroller 31, as best shown in FIGURE 2. The

. separation of the collagen tape on godet 21 is controlled by movingthe axis of the auxiliary roller 31 with respect to the axis of thegodet. The roller 31 pivots on the hinge pin 26 and may be securelyfixed in any position by the set screw 28.

The godet 21 is driven at a speed of about 10 r.p.m. At 10 r.p.m., thelinear rate of tanning is about'30 inches per minute. The collagen tapefrom a tensioning device 35 passes three times around godet 21, thethree loops providing sufficient time in the bath 41 to wet out thecollagen tape well with the tanning solution.

Godet 22 is driven at 11 r.p.m. and, therefore, produces a 10% stretchin the tape between godet 21 and godet 22. The amount of stretch in thisstage may be increased or decreased by varying the relationship betweenthe speeds of godet 21 and godet 22. It will be noted that the strand iswrapped around godet 22 three times. The stretching between godet 21 andgodet 22 provides orientation of the drying collagen tape and improvesthe tensile strength.

Conditions may, for example, be controlled so that the godet 21 isoperated at 10 r.p.m., godet 22 is operated at 11 r.p.m., and godet 23is operated at 12 r.p.m. Under these conditions, one would obtain, inaddition to the 10% stretch between godets 21 :and 22, another 10%stretch between godets 22 and 23.. The over-all stretch may be variedfrom about 10% to and at the present time, the upper limit of stretchappears'to be about 20% The moving collagen tape may be continouslytreated at godet 21 and godet22. The solution 41 in the tray 14 may bean alkaline aqueous solution of a polyhydric phenol and/or quinone suchas: pyrogallol; resorcinol; hydroquinone; 2,24,4''-tetrahydroxybenzophenone; 1,2-, naphthoquinone; l,2-naphthoquinone-4sulfonic acid sodium salt; 1,4-naphthoquinone; p-toluqu-inone;1,2-anthraquinone; or mixtures, of these compounds. Polyhydric phenolsand quinones that are most effective in the tanning process of thepresent invention are those which have an unsubstituted positionadjacent to the oxygen function.

" In addition to the polyhydric phenol 'or quinone, the.

solution 41 may contain a small amount (about 0.5%)

of a chelating agent, e.g., the disodium salt of ethylene diaminetetraacetic acid, to associate with any metal contaminants. A strongreducing agent such as formaldehyde 7 can be used in the bath to deteroxidation.

Thetconcentration of polyhydric phenol and/ or quinone in the bath (41)is from about 0.2% to about 2.0% and the preferred polyhydric phenol ispyrogallol. If this bath (41) is acidic or neutral, the collagen tapewill pick up too much Water. It'is helpful, therefore, to adjust the pHof this bath to about 7.5-10.5 with an alkali such as ammonium hydroxideor sodium hydroxide. Excellent results have been obtained when the pH ofthis tanning bath is 8.3.

The collagen tape passes from the tanning bath 41 around the idlerpulley 30 and then through the drying tube 16. This drying tube has across-sectional area of about 2 to 3 square inches and is about 16inches in length. Air, heated to about 150 F. is circulated through thetube 16 at the rate of about 600 cubic feet per minute.

The dried collagen tape from the tube 16 passes over an idler pulley 29,is wrapped three times around godet 22, and is wet out in the secondtanning bath 42. The, bath 42 contains a basic trivalent chromium saltsuch as chromium (III) sulfate or chloride, the sulfate beingpreferred.Bath 42 also contains an aldehyde such as: form-w aldehyde,acetaldehyde; furfural; glyoxal; succindialdehyde; inalonic dialdehyde;glutaraldehyde; etc. Formaldehyde is preferred. Bath 42 contains, e.g.,an aqueous solution of chromium (III) sulfate and an aldehyde such asformaldehyde or glyoxal, or mixtures of the two. The concentration ofchromium as chromic oxide is about 10 grams per liter, the concentrationof formaldehyde and/ or glyoxal is about 0.10% to about 0.32% and the pHof the bath is about 2.0-3.5 (unbutfered). If the amount of aldehyde isgreater than about 0.32%; the tensile strength of the strand drops andif the amount of aldehyde is less than about 0.05%, the in vivoabsorption of the strand will be rapid. In pasing through this bath, thecollagen tape absorbs about 1% by weight of chromium as chromic oxide.It has been noted that the optimum wet tensile strength and dry knotstrength of the finished strand is obtained when the amount of chromicoxide in the strand to about to F. is circulated through the tube 17 atabout 300 cubic feet per minute and air-heated to about F. and thencirculated through the tube 18 at about 450-600 cubic feet per minute. 7

- The collagen tape from the bath 42 is rounded and shaped by contactwith a false twister 19 of the type illustrated in FIGURE 3. This deviceautomatically im- 7 parts aso-called false twist to the strand, a falsetwist being a twist whose direction on one side of a point of contact isreversed on the opposite side, thus cancelling the twist. The twistingcycle is most effective when the collagen tape is in the wet state, andthis may be controlled by dripping water on the tape from the jet 20.The strand may' alsobe lubricated just prior to contact with the falsetwister with distilled water which is added through the jet 2 4. Whenthe twist backs up to the pulley 34, as the wet tape emerges from it, agradual tapering effect of the strand takes place, which rounds it out.The circular shape of thestrand remains after the twist is cancelled.The false twister is operated in the range of .150 to 1000 r.p.m.

on the apparatus illustrated in FIGURE 1.

It is important that the water added through the jet 20 and the velocityand temperature of the air in the drying tubes 17 and 18 be controlledso that the wet tanned tape is sufficiently dry when the strand contactsthe false twister 19 to avoid deformation. This results in an improvedcircular cross-section.

The round collagen strand passes from the false twister 19 around theidler pulley 36 and may contact with a solution from the jet 25 flowingdownwardly in a direction opposite to the direction in which thecollagen strand is moving. The solution from jet 25 isan aqueoussolution of from about 0.08% to about 0.3% formaldehyde adjusted to a pHof about 9. If the concentration of formaldehyde is less than about0.08% or if the tanning at jet 25 is eliminated entirely, the finishedcollagen strand will be absorbed more quickly when implanted in bodytissues. If the concentration of formaldehyde is greater than about0.3%, the finished collagen strand will be brittle and have poor dryknot strength.

The wetted out strand from the jet 25 passes through the drying tubes 18and 17 around the idler pulley 33 and returns through the drying tubes1'7 and 18 around idler pulley 40. When the godet 23 is operated at 12r.p.m. to produce about stretch between godet 22 and godet 23, thetension on the finished strand as measured by the tensiometer 44 isabout 1500 grams. The dry tanned and rounded strand is removed from thegodet 23 by the take-up spool 13 at about 36 inches per minute. Thefinal strand, under the operating conditions described above, has adiameter of about 14.5 mils (sutures size 2/0).

It has been observed that atmospheric humidity, a variable during thespinning of a strand, plays an important part in the stretch andthefinal tensile strength of the strand. The humidity is preferablycontrolled by encasing the spinning operation within the smallestpractical enclosure into which air of controlled humidity may beintroduced. Superior uniform strands may be obtained when the relativehumidity is maintained at about 40%.

The continuous processing of collagen tape to obtain a unitary strand ofoutstanding properties will be illustrated by the following examples. Byway of contrast, several additional examples are provided to demonstratethat tanning of collagen with individual reagents, namely, a chromiumsalt, formaldehyde and pyrogallol, results in products having in vivotensile strength unsatisfactory for a surgical suture. Throughout thespeci: fication, all quantities are expressed in parts by weight unlessotherwise indicated.

EXAMPLE I A collagen tape approximately 4 mils thick and 60 mils widecontaining 192 individual filaments is processed The speed of the godets21, 22 and 23 is maintained at 10.0, 11.0 and 12.0 r.p.m., respectively.A solution of 0.4 part of pyrogallol, 0.1 part tetrasodiumethylenediaminotetraacetic acid and 99.5 parts of deionized water is adjusted topH 8.3 with ammonium hydroxide and placed in the tray 14 (bath 41).

A solution of chromium (III) sulfate comprising 0.8 part of chromium aschromic oxide, 0.5 part of lactic acid (85%), 0.24 part of formaldehydeand 98.46 parts of deionized water is adjusted to pH 2.7 with sodiumhydroxide and placed in the tray (bath 42).

A solution of 0.16 part of formaldehyde and 99.84 parts of deionizedWater is adjusted to pH 9.0 with ammonium hydroxide and placed in areservoir feeding the passes to the godet 21 and is wrapped three timesaround the godet and idler 31, thelatter being immersed in the bath 41.It takes approximately fifteen seconds to travel one wrap so that thetotal exposure to the solution 41 is about 45 seconds. The pyrogalloltreated strand then moves into the drying tube. 16 and is subjected to acurrent of warm air heated to 60 C. The partially dried strand from thetube 16 then passes over the idler pulley 29 and is wrapped three timesaround godet 22 and auxiliary roller 32. At this time, the moving strandcontacts the solution 42 in container 15.

From the solution 42, the strand travels to the top of the drying tube17 Where it contacts a stream of deionized water dripping from the jet20. This serves to saturate the strand with water for better bondingduring twisting and also helps to remove excess chromium salts. As thestrand moves downwardly through the drying tubes 17and 18, it meets acountercurrent stream of .warm air at about. 60 C. and is twisted by thefalse twister 19, which is rotating at approximately 300 r.p.m. Justbefore the strand enters the false twister, it is lubricated withdeionized water from the jet 24. This prevents abrasion during theuntwisting process. The now rounded strand is next washed with thealkaline formaldehyde solution from jet 25 and finally dried by a doublepassage through the drying tubes 17 and 18. The finished strand is takenup on the godet 23, five to ten wraps being required to preventslipping, and is stored on the take-up spool 13. In the processdescribed above, about 10% stretch is applied between godets 21 and 22and another 10% stretch is applied between godet 22 and godet 23. Theproperties of the product so obtained are summarized in Tables I and II.

EXAMPLE II Solution 41 at godet 21 Parts Resorcinol 0.6 Deionized water99.4

Mixture adjusted to pH 10.3 with ammonium hydroxide.

Solution 42 at godet 22 Parts Chromium (III) sulfate (as chromic oxide)0.8

Formaldehyde 0.24 Glyoxal 0.32 Water 99.36

Mixture adjusted to pH 3.5 with sodium hydroxide.

Solution dripped on strand from jet 25 Parts Formaldehyde 0.32 Deionizedwater -i 99.68

'Mixture adjusted to pH 6.0.

The tape was wrapped six times around godet 21, five times at godet 22and nine times around godet 23. In all other respects, the conditions ofExample 11 were identical with those described in Example I above. Theproperties of the product so obtained are summarized in Tables I and II.

EXAMPLE III A suture material is prepared exactly as described .inExample II above, except that the solution 41 at godet 21 is a solutionof 0.6 part of hydroquinone dissolved in 99.4 parts of deionized Water.The pH of this solution is adjusted to 10.3 with'ammonium hydroxide. Theproperties of the product so obtained are summarized in Tables I and II.

EXAMPLE 1vv I A strand is prepared by the method described at Ex- 7ample I. The following solutions are used:

Slution 41 at godet 21 I Water atpH 10.3 (ammonium hydroxide).

Solution 42' at godet 22 V Parts Chromium (HI) sulfate'(chromic oxide)1.0 Formaldehyde 0.32 Deionized water 98.68

Mixture adjusted to pH 3.5 with sodium hydroxide.

Solution dripped on strand fromj jet 25 Parts Formaldehyde -4. 0.32Water 99.68

Mixture adjusted to pH 5.6 sodium hydroxide.

The strand so obtained is then immersed for one hour in a solution of1.0 partp-benzoquinone and 99 parts of distilled water. The strand isrinsed in acetone and airdried. The properties of the product soobtained are summarized in Tables I and 11.

EXAMPLE V Extruded collagen multifilament was tanned in a basic chromiumsulfate bath containing 1.25 percent Cr O No formaldehyde or polyhydricphenol was used in the tanning process. Properties of the product areset forth in Tables I and II. p

r EXAMPLE v11 Extruded collagen multifilament was tanned ina bathcontaining 0.15 percent formaldehyde. No chromium or polyhydric phenolwas used in the tanning process. Tables I and II reveal properties 'ofthe product so'obtained.

TABLE I Tensile Strength (Grams/ Denier) Example Denier Diameter Dry DryWet Straight Knot Knot 15. 0 3. 93 2. 00 1. 25 15. 5 3. 16 1. 61 1. 5515. 6 3. 24 1. 36 1. 39 14. 4 3. 40 1. 61' 1. 48 V 15.3 3.31 1.74 1. 33VI (only C1) 1,390 2. 6 1. 5 1.2 VII (only ECHO) 1, 440 2. 41 1. 39 0.98 Catg'ut l, 210 14. 0 3. 60 2. 40 1. 20

TABLE II [In vivo absorptionin pounds] Days Implanted Example 5. 5 3.2 1. 9 .9 4.5 4.6 '3.6 3.5 0.6 .1 4.8 4.4 3.9 2.9 0.9 .4 4.5 4.6 4.3 4.03.9 1.7 V .7 5.6 5.0 3.9 4.3 3.0 0.8 VI (only Cr) .6 1.0 p VII (onlyECHO) 4. 0 1. 6 Catgut 8. 2 5. 3 4. 6 3. 9 3. 3 2. 5 1. 4

7 EXAMPLE VIII Another series of experiments was carried out todetermine the separate eitects of chromium sulfate, pyrogallol, andformaldehyde'upon an extruded collagen tape. Each reagent was applied'by the procedure described in Example I, above. In experiments 1 through3, pyrogal- 101 was applied from the bath 41 and distilled wateradjusted to pH 3.5 was applied from the bath 42. In experiments 4through 6, distilled water at pH 8.3 was placed in bath 41 andformaldehyde at pH 3.5 in bath 42. 'In experiments 7 through 9,distilled water at pH 8.3 was placed in bath 41 and chromium sulfate atpH 3.5 in bath 42. In all ten experiments shown below, lactic acid waselminated from bath 42, jets 20 and 24 were not used and the strand waswet out with an aqueous solution of 0.3 percent formaldehyde (pH 8.5) atthe jet 25. The following results were obtained:

Experi- Levels of Treatment Bath merit Compound pH PyrogallolFormaldehyde Chromium sulfate Combination run 1 1 First bath: 1.5%pyrogallol, C12(SO4)s-l-O.3% HCHO, pH 3.5.

Tensile strength pH 8.3; Second bath= 1.0%

Denier et Knot y Straight 1 First bath:1.57 pyrogallol pH 8.3' Secondbath-:10? 0r2 s0. 8+0.3% HdHO, pH 3.51 a

In vivo tensile strength Days Sample N o.

2. 08 1. 74 1. 54 I. 66 1.14 1. 90 l. 2. 2 1. 89 1. 96 1. 70 2. 57 2. 12. l9 1. 07 2. B6 1; 31 1. 69 2. 12 1.25 4. 59 2. 55 3. 09 2. 21 3. 203.84 3. 91 3.10 2. 49 21. 6 2. 81 2. 04 1. 13 1. l8 3. 93 2. 99 3. 1O 1.97 4. 40 2. 42 2. 56 l. l. 67 6. 66 5. 24 5. 35 4. 65

4 In connection with the data tabulated directly above, it is clear thatthe in vivo and in vivo tensile strength values for the tanned sampleNo. 10 are indicative of an excellent material.

EXAMPLE IX Sutures prepared according to the method of the presentinvention contain polyhydric phenols and/or quinone reduction productsthat are chemically combined with the collagen. A quantitivedetermination of the amount of ,polyhydric phenol or quinone that ispresentin the finished suture may be made by the following method.

. v A IO-milligram sample of .a polyhydric phenol and/or quinone tannedsuture, is placed in a test tube and 1 milliliter of sodium borohydridesolution is added- The solution-of sodium borohydride is prepared bydissolving 0.60 gram of sodium borohydride in 20 milliliters ofdistilled waterand adding one pellet of sodium hydroxide.

This solution is prepared fresh for each group of samples. The test tubecontaining the suture to be analyzed and borohydride solution is heatedover a Bunsen flame until the suture is dissolved. The contents of thetest tube are then neutralized with concentrated sulfuric acid and thetest tube is heated to decompose any excess sodium borohydride solution.The reaction mixture so obtained is cooled and diluted to 3 milliliterswith distilled water. One milliliter of a vanillin reagent, prepared bydissolving 7.5 grams of vanillin in 50 milliliters of ethyl alcohol, isadded and the mixture is diluted with 79% sulfuric acid to 23milliliters. After 20 minutes, the absorbance at 520 mu is compared witha reagent blank using a Beckman D.U. spectrophotometer and fourstandards containing 0.01, 0.02, 0.03 and 0.04 milliliters of thepolyhydric phenol or quinone subject to the analysis, such as apyrogallol solution, prepared by dissolving 0.130 gram of pyrogallol in4 N sulfuric acid to a total volume of 100 milliliters.

The absorbance values are plotted against the volume of standard and thepercent polyhydric phenol or quinone in the sample is calculatedaccording to the formula K A X 100 Sample weight (mg) Mu2,2',4,4'-tetrahydroxybenzophenone 520' 1,2-naphthoquinone 5701,4-naphthoquinne 575 p-Toluquinone 560 1,2-anthraquinone 545 Resorcinol510 Accurate and reproducible results are obtained with the foregoingprocedure with phenols and with quinones, with the exception ofbenzoquinone. A'separate procedure is followed in determiningbenzoquinone content of a suture obtained in accordance with thisinvention. A SOO-milligram sample of a benzoquinone-tanned suture isplaced in the test tube. Five (5) milliliters of hydrochloric acidsolution (2 N) are added to the tube. The tube and its contents areheated over a Bunsen flame until the suture is dissolved. The contentsof the tube are cooled, 5 mls. of ethanol are added thereto, and theresulting solution is shaken. The solution is transferred to a 25 m1.volumetric fiask and is made up to volume with distilled water. Theresulting solution is filtered into a 50 ml. beaker. Ten milliliters ofthe filtrate are added to a 25 ml. volumetric flask, whereupon 1 ml. ofpyrogallol solution (1% in water) and 10 ml. of ethanol are added.Distilled water is then added to the 25 ml. level of thefl-ask. Afterone hour, the absorbance at 425 mu is compared with a reagent blankusing the said spectrophotometer and three standards containing 0.01,0.02 and 0.03 milliliter of a benzoquinone standard solution. Thestandards are prepared by dissolving 100 milligrams of benzoquinone in100 milliliters of distilled water.

The absorbance values are plotted against the volume of the standard andthe percent benzoquinone in the sample is calculated according to theformula:

Percent benzoquinone:

Density reading at 425 mu Factor Weight of sample (mg) milligrams ofbenzoquinone Factor: absorben y unit a night.

id 0.92%, and preferably from about 0.30% to about 0.70% polyhydricphenol and/ or quinone as determined by the foregoing analyticalmethods.

By way of contrast, extruded collagen strand and hide were treated withresorcinol and formaldehyde by the procedures given in the followingexamples. As shown therein, the products obtained therein containsubstantially larger percentages of polyhydric phenol than about 0.25%to about 0.92% characteristic of the sutures of this invention. I

EXAMPLE X Extruded collagen tape (40 grams) was added to a solutioncontaining grams of distilled water, 7 grams of resorcinol, 14 grams offormalin and 5.5 grams of sodium chloride. The pH of the resultingsolution was 2.7. The collagen tape was rolled in the solution for 2hours. The pH of the solution was adjusted to pH 1.5 by slowly addingconcentrated sulfuric acid thereto; this was maintained for 3 hours.Additional sulfuric acid was added to bring the pH to 1.0. The collagentape was rolled in the solution overnight (17 hours). The solution wasgradually neutralized with 1.5 grams of sodium acetate and then with0.75 gram of sodium bicarbonate. The collagen tape was then rolled inthe solution, pH 5.5, was washed in tap water for one hour, and wasfinally dried during a 24-hour interval. The treated collagen tape, onanalysis, contains 1.05 percent resorcinol.

EXAMPLE XI The procedure described in Example X, above, was

used in treating 50 grams of wet, fresh, neutral hide. The initialsolution contained:

' Grams Distilled water 100 Resorcinol 3.5 Formalin 14 Sodium chloride2.8

On analysis, it was determined that the/treated hide contains 1.18percent resorcinol.

EXAMPLE XH Extruded collagen tape (4 grams) and wet, fresh, neutral hide(25 grams) Were tanned concurrently. The tape and hide Were added to asolution of;

The pH of the solution was adjusted to 2.0 with concentrated sulfuricacid. The tape and hide wererolled in the solution for 2 hours.Additional sulfuric acid was added to reduce the pH to 1.5. Again, thetape and hide were rolled for 2 hours, and held in the solutionovernight (17 hours). The pH Was adjusted to 1.0 by the addition ofsulfuric acid, and the materials were rolled for a 2-hour period.Further adjustment of pH to 0.6 was made with more of the acid. Thematerials were held in the solution overnight (17 hours). Sodiumbicarbonate (l.3 grams) was added slowly to the solu tion, and the tapeand hide were rolled in the resulting mixture for 2 hours. The materialswere again held overnight. Additional sodium bicarbonate (1.3 grams) wasadded. The resulting materials were held over- Finally, the tape andhide were washed with distilled water for 3 hours. Upon analysis, it wasdetermined that the resorcinol contents of the tape and hide are,respectively, 1.23% and 1.37%.

It will be understood that the process described above may be utilizedin the preservation or" other collagenous materials such as leather, theuseful life of which is frequently'shortened by the attack ofmicro-organisms and enzymes produced by such micro-organisms.

' The method of treating collagen articles with quinones .those skilledin the art that changes and modifications can be made without departingfrom the spirit or scope of the invention, and it is intended in theappended claims to cover such changes and modifications.

What is claimed is:

1. In a method of tanning collagen that has been acidswollen, extrudedand reconstituted; the steps of conphenol is pyrogallol.

3. The method of claim 1 in which said polyhydric phenol ishydroquinone.

4. The method of claim 1 in which said polyhydric phenol is resorcinol.

5. The method of claim 1 in which said aldehyde is formaldehyde.

6. The method of claim 1 in which said aldehyde is glyoxal.

7. The method of claim 1 in the form of a tape.

8. In a method of tanning collagen that has been swollen, extruded andreconstituted; the steps of contacting said. collagen with a solution ofa polyhydric phenol selected from the group consisting of monocyclic anddicyclic polyhydric phenols, and subsequently contacting said collagenwith a solution of an aldehyde and 'a basic trivalent chromium salt.

9. In a method of tanning collagen that has been swollen, extruded andreconstituted; the steps of contacting saidcollagen with a solution ofan aldehyde and a basic trivalent chromium salt, and subsequentlycontacting said collagen with a solution of a polyhydric phenolselecte'dfrom the group consisting of monocyclic and dicyclic polyhydricphenols.

10. In a method of tanning a collagen suture obtained which the collagenis by extruding and reconstituting acid-swollen collagen; the steps ofcontacting said suture with an alkaline solution containing pyrogalloland'subsequently contacting said suture with an aqueous solutioncontaining about 0.24 part of formaldehyde, about 0.8 part of chromiumIII sulfate calculated as chromic oxide, and having a pH of about 2.7. I

11. An aldehyde, phenol and chrometanned collagen article obtained byextruding and reconstituting acidswollen collagen, said articleanalyzing from about 0.25% to about 0.92% by weight of a polyhydricphenol selected from the group consisting of monocyclic and dicyclicpolyhydric phenols, and characterized by a chromiurn analysis from about0.5% to about 1.5% by weight chromic oxide.

12. An aldehyde, phenol and chrome tanned collagen suture obtained byextruding and reconstituting acidswollen collagen, said suture analyzingfrom about 0.25 to about 0.92% by weight of pyrogallol, andcharacterized by a chromium analysis of from 0.5% to about 1.5% byweight chromic oxide.

13. An aldehyde, phenol and chrome tanned collagen suture obtained byextruding and reconstituting acidswollen collagen, said suture analyzingfrom about 0.25% to about 0.92% by weight of resorcinol, andcharacterized by a chromium analysis of from 0.5% to about 1.5% byweight chromic oxide.

14. An aldehyde, phenol and chrome tanned collagen suture obtained byextruding and reconstituting acidswollen collagen, said suture analyzingfrom about 0.25

.to about 0.92% by Weight of hydroquinone, and characterized by achromium analysis of from 0.5% to about 1.5 by weight chromic oxide.

7 References Cited in the file of this patent UNITED STATES PATENTSOTHER REFERENCES OFlaherty et al.: The Chemistry and Technology ofLeather, pages 91-94, 254-255, 261, 267 and 273-275, published 1958 byReinhold Pub. Co., N.Y.C.

Chen: Syntans and Newer Methods of Tanning, The Chemical Elements, SouthLancaster, Mass., 1950, pp. 87-96.

1. IN A METHOD OF TANNING COLLAGEN THAT HAS BEEN ACIDSWOLLEN, EXTRUDEDAND RECONSTITUTED; THE STEPS OF CONTACTING SAID COLLAGEN WITH AT LEASTTWO DIFFERENT SOLUTIONS, ONE OF SAID SOLUTIONS CONTAINING A POLYHDRICPHENOL SELECTED FROM THE GROUP CONSISTING OF MONOCYCLIC AND DICYCLICPOLYHYDRIC PHENOLS, AND ANOTHER OF SAID SOLUTIONS CONTAINING AN ALDEHYDEAND A BASIC TRIVALENT CHROMIUM SALT.